Telegraph repeater



Aug. 2, 1960 .1. l.. HYsKo 2,947,816

TELEGRAPH REPEATER Filed Aug. 22, 1956 6 Sheets-Sheet 1 Aug. 2, 1960 J. L. HYsKo frm-:GRAPH REPEATER 6 Sheets-Sheet 2 Filed Aug. 22, 1956 6 Sheets-Sheet 3 Filed Aug. 22, 1956 Il; nlll AVANA.;

- y )Pebl Rm M m5 o ENV U A WL M ---u @d 2 V B xx- @dfi 6 Sheets-Sheet 4 WJ Wwf J. L. HYSKO TELEGRAPH REPEATER Aug. 2, 1960 Filed Aug. 22, 1956 l An vvv l AVAAV n Ik Il Il Aug. 2, 1960 J. L. HYsKo TELEGRAPH REPEATER avf... e. @W25 A r Tom/EV Aug. 2, 1960 .1. L. HYsKo TELEGRAPH REPEATER 6 Sheets-Sheei'; 6

Filed Aug. 22, 195e al. @n ATrbR/VE w ...El

Ia direct-current telegraphlrepeaterf ircu nited States Y 2,941,316: a TELEGRArH RaraArnia vv ,zal ration of New York shift,- carrier-current,v rnamialv telegraph switching system and-tparticularlyto an arrangement wherein a frequencyshitty carriercurrent telegraph circuit y isi terminated at teltypewriter switchboard and at a subscriber station-inV direct-current terminations .andA in whichtransmission 20 over the line between the switchboardvand'the subscriber station is-on acarrierbasis; Such a system is thesubjet- .matter ofa patent application, Sett-iai. No 2l86,9 98, file d ,inlthe. names of L.- Arf Gardner- -andJLrI -Iysloingthe United States Patent Otlice; on May 9, l9;5 2,fI10WRate/11t 25 a? frequency-shift carrierfterrninal; located onv the;l sub- 30 -sc-riberfs premisesover acarrien .facility to arfrequencyshift carrier terminallocatedfat a ;teletypewrit`er switching stationV and through a Vtoll subscribers line: circuitL tozthe teletypewrite'r switchboard; The, circuit-'of the" .presenti ap- :plication differs from' thelcircuitof the-patentl identified 35 -inxthe foregoing in that itis designed tofope'raterove'r .a ffacility in which intermediate repeating-is requirdrx This i's;` achieved by interconnecting two,` frequency-shift carrier 'telegraph` channel terminals; l resembling theeo'ns .located atxthe-subscribe stationf'ancl'lat-thevteletypewriter swit'h- 40 'f board inz-the patent application identified in the: foregoing, 'inf a ffback-toL-back connection, soithat'fA signalsy may bey `repeated from one ,toy the other without the use of aldirect fcurrentrnagneticrelay repeater.f In general, the present Ybaekato-backi repeaters' may be effectively employed-'lat 45 intermediate points for Athetlzlreeffollowingpurposes:

r'I (l) Totransfer' signals from an vopen wirercircuit-toaw subscriber circuit, where-A the channels* occupyv diiernt different,terminationswithoutrequiring that th" vg eral single'channel.- f

An object of theinventionhisthe-direct"interconnecn tion` of two frequency-shift car 'fel raphteijninting circuits backitoback, at" aninterii diatei'p'eating int, without the' necessity foi-3 inter n Attention is' calld'tdth ac thatY operating direct-current crcmtr .isha Hy'ska-summif, NJ., assigner tenen Telephone invention relatesi toj a direct-current', frequencj- `15 ploye "hier "diei-e' ail 2,947,816. Pstsntsd Auer@ 126i? ice directfcurrent signals, incoming from the receiving branch ofthe frequency-shift' circuit, andto impress rn` in suitable formi on the' transmitting .branchfofV fije q `ncy's h ift circuit, whichis potential; (iontlfo'lled.y 1re m invention obyiatestheneed forth-e directcurrent relaylrepeat'er at an intermediate pointv whereattw carrier-current frequency-shift terminating repeatersj nnected back-to4back. inventiqnmy be,nndestodrfromthefoll ing description when "readj wi 'reference to'the associated drawings 'in 'Whichfthe invention is' presently incorporfat `It isto be understood, however, thatthe. invenmay' be incorporated in' other forms, whicliwillbe suggested from a consideration ofthe following. I n'the dirayvingsi--,

Figs', 1"! 2 taken together, WithFig. 1 disposredwto the left of Figi` 2, shdwthesystem of the` presentinventO'l'l'; v

4-Fig's'l ,31 and' 4 show ,the details ofY carrierl terminals emriaf back-to-ba'clrv connection; l v Y, igs. 5 and 6- show the details of carrier terminals plqy'ed atthe switchboard and at the subscriber station, es'pectively.

'Reifer'inow to Fig. V1 and Fig. 2, with Figtjl disposed to' thleft of Fig, 2. The major units` of the systems iiir'stbe identiiied and the manner in which theyv are Y interconnected will be described broadly. At theI upper left in Fig. 1 the elements of ateletype- Writerrswitchboardare shown. These comprise air-jack 1' i s, represe ntative of the terminations of a vvery 'largeinniber of circuits-inthe switchboardto which-the ritffacilities may be connected by means of `attele- "rite'r Jcord Ycircuit, which latterA isV ;ir 1c iiatec 1; y by; a @d ,ecthgle' together -Withrluss BGl andfPGZ eirlr pctiv`e ,cords. The'teletypewriter cord cirupon thel subscn'beritoll line circuitand the'otherr circuits with vf/hichitconnects. Whenethe subscriber toll ungenfcui sho l. liii Fis-, 1 iS employ@ the; Cordfcircuit; of Fig. ofPatent'fNoL1,965,383 granted .to C. C; Lane, Jylyilv", l9l4g'oithe cord'circuit of Fig. 3 o'ff'Patent No. 2,222,622 Y grggulted.-tolNV. V. Iig-Large,- Novernber 26, 1944))A 'I lybefemployed; Jackf I2 and lamp L are the jack and lamp in` which the subscribertoll line circuit 'shovvnat'th'eupper right in yFig.1 is terminatedat vthe 'tchboard The diagonal spurs` connected.to ther-jack are duplicated at other positions in tli switchbb" The"subscriber`tollY line circuit cotnprifsagroupof fv'eLrelay's and otherincidentalapparatusin the upper iifejgeater-station, YwhichV is intermediate' the" switchboard and the subscriber station, where it?connectsfthrugh ,tra

i' captioned nectaiigle. Cartier Terminal 3v1s m accordance with Fig. 3 and is connected through another transformer TRS3 to a line facility which extends to the subscribers premises shown in the lower portion of Fig. 2. Here the line connects through transformer TRS4 and another frequency-shiftcarrier terminaL'Carr-ier Terminal v2, to the subscriber teletypewriter station circuit, shown atv the lower right in Fig. 2. Carrier'Terminal 2 is in accordance with Fig. 6. y

With respect to the drawings, Fig. l and Fig. 2 are identical with the arrangement disclosed in the aboveidentified patent granted yto L. A. Gardner and l. L. Hysko except for the Carrier Terminals 3 and 4, shown in the lower portion of Fig. l, and their interconnections. That is to say, in the arrangement of the patent, the external connection of the carrier terminal such as Carrier Terminal 1, at the teletypewriter switchboard, shown `in the upper portion of Fig. 2, is made directly through a line facility to a carrier terminal such as Carrier Terminal 2, located on the subscriberls premises, shown in lthe bottom portion of Fig. 2 without passing through the two Carrier Terminals 4 and 3 located at the intermediate telegraph repeater station. These two frequency shift carrier terminals, Carrier Terminals 4 and 3 are interconnected in what is known as a back-to-back manner. What is meant by this Will be described hereinafter.

The present system, it will be observed, in addition to the Carrier Terminals 3 and 4, interconnected back-to- 'back comprises three major circuit units, namely the frequency-shift carrier terminal circuits, the subscriber toll line circuit and the subscriber station circuit. These are described in the patent identified in the foregoing. However, they will be described here for the convenience of the reader.

Refer now to the subscriber teletypewriter station circuit at the lower right in Fig. 2 the operation of which will now be described in detail. The subscriber station `equipment may be arranged for attended or unattended service. The arrangement shown in Fig. 2 is for attended service. In this arrangement when the circuit is idle, as shown, a path may be traced from the grounded cathode of tetrode V53, lthrough the tube to its anode, and conductor TR which is connected through contact 1 orf-switch 9 to the subset or ringer 10 where it extends through resistor RSZ and the windings of two ringer magnets RM1 and RM2, in series, to positive battery, which may be, for instance, +130 volts.

When the subscriber station is to be called from-the switchboard, ringing current is applied at the switchboard in a manner to be described. This current may be 20 cycles, for instance. This is translated in the carrier circuit'into transitions'between frequencies f1 and f2 at 20 cycles` and responsively intothe activation and inactivation of tetrode V53 in Carrier Terminal 2 at 20 cycles. Current no-current pulses at 20 cycles will pass through the ringer magnets RM1 and RM2 in the subset 10, to operate the ringer. Y

When the subscriber station is in the idle condition as shown, a circuit may be traced from ground, not shown, in thermodulator and tuned circuits through the cathodeanode path of oscillator 20, resistor RS3 and conductor l SS to contact 3 of switch 9 which is open for the idle condition of the subscriber station. During the idle condition, therefore, no oscillations will be produced in the oscillator circuit of Carrier Terminal 2-and no signals will lbe transmitted through the send amplifier and gain control, the send filter 26 and transformer TRS4 to'the line. This, as will be rnade clear hereinafter, produces the third or no-carrier signaling condition employed for calling and supervisory purposes. l Y

l After the subscriber station has been turned over to the customer for service, the'teletypewriter circuit plug PTY is connected at all times to theteletypewriter jack TTY.

instance, be 11S-volt lalternating current, is open at con-- tact 4 of key 9.

In response to the ringing of the station, theattendantactuates switch 9 to its lower position closing contact 4'y and energizing the teletypewriter motor. When switch 9 is actuated to its lower position, contact 1 is opened disconnecting the subset or ringer 10. Contact 3 is closed which connects positive battery, such as positive 130 volts, through resistor RS3 to the anode o-f oscillator 20. Contact 2 of switch 9 is closed which connects lead .TR throughl resistor SR1 and either through contact 1 of jack TTY to positive battery which may be,\for instance, positive 130 volts, or through the teletypewriter cord circuit, when the cord is connected to the TTY jack. Under this condition, contact 1 of jack TTY is open, its contact 2 is closed and the circuit is extended through the tip of jack TTY, tip of plug PTY, teletypewriter transmitting contacts STI'Y, contacts of break key B,KWind ing of selector hold magnet HM, lsleeve of plug PTY, sleeve of jackl TTY, and'contact 2 of jack TTY to the same positive battery. The anode of tetrode V53 and the grid of modulator drive triode 23 are connected in parallel.

After the operation of switch 9, permutation code signal combinations, comprised of signal elements f1 and-f2, defining letter, number and other teletypewriter characters and other'combinations which control the teletypewriter in performing functions such as spacing, line feed carriagereturn, etc., may be transmitted from the switchboard and impressed on the selector magnet HM of the teletypewriter at the subscriber station, which will responsively type the character or perform the. function. This will be made clear hereinafter.

' 'Intransmitting from the subscriber station toward the switchboard the-station' attendant will operate the teletypewriter keys to ractuate the teletypewriter transmitting sending contacts STI'Y. "As the contacts are actuated the path through the teletypewriter cord circuit will be opened and closed. During the closed interval, current will ow through the teletypewriter and the anode-cathode path of tetrode V53. During the contacts open periods, no current willflow. Thepotential impressed on the l'input of the modulator drive tube 23 will responsively change so that it conducts forthe closed or marking condition and is cut offfor theopenor spacing condition. To anticipate the detailed Vdescription of the carrier terminals and of subscriber toll line circuit, tofollow hereand finally through conductor S into the toll subscriber in which two such terminals .function in a Asystem in` which Vline circuit. Supervisory signals are transmitted from' the subscriber station under control of switchv9, which switch produces the no-carrier condition when in its upper position and marking carrierfl when intits lower position. These signals pass through a triode 23' in the receive amplifier, limiter, discriminator and gain control `in Carrier Terminal 1 and areimpressed through conductor RS on i the toll subscriberlinercircuit to control the line lamp L or toimpressconditions through the contacts of jackgJZ to operate supervisorysignal controls, such as recall and vdisconnect signal-controls, in the connected cord. Y VPrelirninary VVto ,a description ,of ;how. the, carrier termithey are interconnecteddirectly without passing through a The teletypewriter motorwhich drives the teletypewriter is not energized sinceits energizing circuit, which. may, for

l elias! .1. tezarfierrmiral 2.

back-to-back4 lconnection will Vbe described. Such a sys- 'tem would involve the -direct connection of Carrier Ter- Refer howto Figs." and 6 withFg. -5 tothe jleft 'of' Fig. 6. In Fig. 5, the toll subscriber line circuit, shown in detail at the upper right in'Fig. 1 is indicated-by a rcc` tangle at the left. andl receiving branches of the carrier circuit shown at the top and Ibottom of Fig. 5 respectively, through trans former TRSl, and the line into Fig. 6, through trans` former TRS4 and the sending and receiving branches of the carrier terminal at the subscriber station to the sub-l scriber station circuit indicated by arectangle at the right er Fig.V 5. y l Y Refer now to Pig. 5. The carrier telegraph transmitter comprises an oscillator having a tuned circuity 21 v in its feedback path. The tuned circuit 21 is tunable to two discrete frequencies f1 and f2, termed the normal and' shifted frequency, respectively. The oscillator 20 generates the normal frequency fl'determined by variable vcapacitor C1 vand the primary coil vL1 of transformer T1,`

which frequency represents the marking condition. Por spacing, the frequency of the oscillator is shifted to f2 by the coupling of additional reactance L12-O2 into 'the tuned circuit. The switching of the added reactance under the control of the varistors 22, 22', whose impedance, high or low, is determined by a bias' direct-current voltage on lead M. l

The oscillator tube 20, which may be half of a twin triode vacuum tube, furnishes the necessary -feedback gain to maint-ain oscillations. The other half of the twin triode, namely tube 20', constitutes a buffer amplifier between the oscillator 20 and the line. The output fromV the ,oscillator tube 20 supplies feedback to its frequency determining tuned circuits 21 througlrresistor vR22 andi Resistor R8'v Winding 5 4 of input transformer T1. serves to suppress parasitic oscillations. d

The oscillating voltage which appears between winding 6--5 of transformer YT1 is applied between the grid and cathode of tube 20, causing a current of the same frequency to' circulate through'the cathode-plate circuit of this tube, which includes condenser C13 and a group of resistances R1, R2 Vand R3 in series with the cathode. The drop in the group Vof resistances R1, R2 and R3 is applied to winding 4-5 of transformer T1 which furnishes the necessary coupling between' the cathode and grid to sustain oscillations. The grid of tube 20 is suitably biased by the -direct-current component of the cathode current through resistor R3. v

For the m-arking'condition, the varistors 22 and 22' are non-conducting or biased to provide a very high impedance, thereby rendering the secondary of transformerv The varistors 22 and 22 function as series switches under the control of modulator" tube 23, which may be half of a twin triode vacuum tube, the other half of which may be triode 23'. The grid of tube 23 is drivenby theV signals originated -in the toll subscriber line circuit in a manner to be described hereinafter. is thus caused to conduct for an outgoing marking signal and to cut off for an outgoing spacing signa-l. d

When modulator tube 23 is conducting, lresistor R15 and the-plate to cathode path lof tube 23'connected It is connected through the sending` the mark- If the net added reactavnceA is capacitive the frequency is shifted to a lower value.- If inductive, the frequency is shifted to a higher value.y

Modulator tube 23 serisfa'rsshntea by resistors R10 ammi. coa;

dition'r 'produces' a potential; at'the plate of tube 23 whichy is negative with respect to the potential .at the .junction of' resistors R\10 and R11. Thisne'gative .potential is impressed between terminal 2 ofFtransfor-mer. T1 and terminal 2 of.v inductance. coil '.L2and is thus impressed across varistors. 22 fand Z2 inlthe non-conductingfdire.

tion. Y

'.For. the spacing condition,y the'tube 23 is. cut orand" a current flows from negative" 13D-volt battery, for. in-v stance, through resistor R-31f, resistor;.R30, resistor R11,

terminalV 2 ofinductance coil-L2, ythrough the topand.v bottom windings'of indu'ctance coil L2 in parallel, varis.-

torsl 22 and 22Y inparalleL windings 1--2fand windingsv 2-3 of transformer T1 in parallel, conductor M' and re= sistor R15 to ground.l .The path .'fromzthe top terminal of resistorRll to ground, `'as just tracedg is `shuntedfby resistor R10. Varistors 22 and 22-are atztheirllow .im-'1 pedance .forthis condition: As a result-l of the'lsecondary of input transformer, .T1 is e'ffectiv'elyfcoupled to'. the reactance'of inductance. coilL2 andl capacitor C2."

This changes the tuning ofthe oscillator circuit which responsively `generates alternating cur-rent atfrequency f2.. Since the voltage currentfor'controlling the imped ance ofthe varistor units is fed into'centertaps 2, 2 jofthe input transformer secondary and of the inductance coil L2, respectively, no disturbing transients are coupledinto theV oscillatorv tunedY circuit.. The marking frequencyA f1-.an'd the spacingffrequency f2V from vthe oscillator Vaiepassed into thefcapacitorv C14:

and through the variable resistory R5 :into the buffer amplilier` 20',l thence through: sending filter 26 andltransformer TRSI over the line to the distant subscriber,sta.

tion. The sending filter 26 is .tuned to the mid-frequency of a' frequency bandbetween. f1 and f2. f Y

Thus, signals are formedbyrshift-ing the carrier equal amounts `aboveV and lbelowthe nominal of the sending and receiving filters. Refer. now -to Fig. 6. A'l-he receivedy an appropriate receiving Ili-lter 31 which `accepts a narrow band of frequenciesrcentered about themarkin'gand spacing frequencies f1 and f2. ofthe channel toY bere-z ceived. :L Like-the sending ilter:;of Fig.y 5 the receiving fi1t'er31of Fig. 6 provides an "impedance transforming structure presenting 600ohms toward th'e .lineand ap'- proximately 140,000 ohms vtoward'tliev grid cathode circuitof the' lirstampliiier stage V51A.- Tubes` V511A, V51B `and V52 form an amplitierlimiter so that the outputof tube V52 remains constant for wide variations .of received level. When the received level is low, tube V52 does all of .the limiting. The 1-megoh'm resistor RSS-in' serieswith its grid prevents the grid from going positiveV and so confines swings in Iplate current to the rangefrom 0 to about 10 milliamperes. The out-put therefore is substantially constant for anysignal-level at the inputof; the received filter 31 not exceeding `about minus 50 deci-y bels with respect to one rmilliwatt. When this level is so. high that grid current tends to ow intubes ,V51Aand V51B, these tubes also contribute to Athe limiting action due to the resistance in the grid circuits. Large carrier amplitudes are limited by t-ubeVSlA andy small ampli-` tudes are limited by tube V51B and/or tube V52. l

`The resistor R42 constitutes a gain .control which.is

connected between theplate of tube VSIA and the grid ofK tube VSIB. It provides the means for adjusting the gain of the limiter-amplifier aforementioned. The series grid: resistor R41 serves to4 limit the positive grid swing fory large signals and minimizes thel amount of self-bias vcle-Q veloped across coupling capacitor' C6. This arrangement gives substantiallysymrnetrical limitingV of the carrierk frequency wave form.

` The output from Athe plate`of"tube'Vd5i1yB"is coupled'Y to the' grid of pentode ltube V52." The series" rgrid'res'istor' oscil-i.- -lator vfrequency between .values 'f1 and f2 which areY mid-band:

signals passi through transformer TRS4 of Fig. 6 and are selected .by'

7 R33- limits the. positive grid swing and minimizes, the. amount vof selfi-bias acrossicoupling capacitor CL dueV to. grid rectification.

Ther plate Vcurrent offtube. V52V passes throughy the pri mary side of the" discniminator circuitV 60. The discriminator. consists of two; anti-resonant circuitsV 62 and 6.3 in seriesiwhinhiare tuned respectively to somewhat higher and lower frequencies than f1 and f2, the mark and spacci frequencies,I respectively-- The coils of the two tuned circuitsiziandf areA the. primaries of the two independent onefto-onezratioe transformers T2 land T3, one primary heing tuned'. to parallel. resonance at thefhigh frequency edge of the. channel. band, andthe other being tuned to parallelresonanee-'at the lowy frequency edge of the chanf nel=I band. 'Phe secondary windings of transformers T2 andTfareconnected in series: Reversing switch 61 provides.t means for; reversing the output connections from thefzdiscriminator network.

fWhen the discriminator switchiis: operatedv to the HF-iposition, the'y higher frequency is rectified by rectifier- 64y andthe lower.- byt rectifier 65; resulting in direct-current voltages: appearing-across points XY and YZ, respectively. AtV the mid-band frequency the two voltage outputs are balanced giving zero-output. When the, higher frequency is being receivedv its voltage is dominant and when the lower; frequency signal` is beingreceived its voltage, that is thef direct-current. voltage produced by it, isV dominant. It follows that when the higherlfre'quency is received, voltageXY'predominates andl the` grids of tubes-'V53v and V54 arci positive with` respect to7 their cathodes, and when butV this voltage,or1 the greater part of it, is alternately' shifted betweenrk the input terminals 3I1 and 2 4-of the discriminatortransformer,.depending on whether' a markinglorspacing frequency'is` received; Fundamentally, the limitingzaction is secured by producing an amount ofi am# plication in tubesxVSl'A and V51B'which is far in excess'of thatrequir'ed? to obtain the neededvoltage acrossl terminal andterminalYZ and` then severely curb-ing the magnitude :of their outputs; Due to this action, variations in'levelfchangeiaicti equally the marking and spacing frequenciesr andr cause nov signalf distortion. InA other words,` frequencyeshift: operation v gives" extremely effective.v

level' compensation.

'Ihe rectified signalslA are passed through thelow-pass lterl 6 61consis'ting`l ofinductance coils 67A and condenser 68- The low-'passi filter:` has1acut`off frequency near 40 cyclesK-fand-serves to 'remove-carrier ripple and to attenuate interference arising! from extraneous frequency compone'n'ts differing from the carrier' ffequency by more than 40' cycles. A balanced' low-pass filter structure without niu-V tualinductance is lused-in orderv tov present Vhigh and nearly equal impedance to ground. This Vprevents -a change inthe tuning of the discrirninatorv when reversing switch 615 is operated for reversing connections from the discriminator. I A positive or negative output may thereby be obtained. by the marking condition; The discriminator switch .61 also permits normal operation with a reversal` f` the mark and space' frequency assignments if desired. The output ofthe low-pass filter is terminated by resistor R71` and is' applied through gridlimiting resistorl R72to the gridsfof output tubes V53I and V54. In order t9 enterlthe demodulated signals'on the grid characteristic:

o'f-1 tubes V53` andVSA4 and thusavoid biased signals', the mean;v of the: markandspaceoutput; voltages from Vthe lowpass; lterg. must be; a few volts negative with respect to the cathodes of tubes V53 and V54;r This is laccomplishedby. adjustment@ the: patenti@meier`4 e9, by. which the positive out-put condition may; be: made tol be of lessi amplitude; than: the. negative: o ut-pjutV condition. The; potentiometer. 6938150. providesl means for` compensating for discrepancies in thediscriminator andA deviations'y in the marking and' spacing frequenciesffrom their theoretical values, also for other biases which may originate in the sendingtermi'nal.

Tubes V53 andlV54; therefore' actin unison as a single switchV whose closing is controlled by positive signals across terminals and whose opening is effected; by

negative signals across the same points, that is', they. arev equivalent-r toareceiving` relay operated by. polar signals;

When signals; are received, thisswitch closes the circuit through the TR lead into thesubscriber stationcir-V cuit permitting current from plus IBO-volt battery, for instance, to'ow: throught-he connected circuit'to the anodes of tubesVS and;V5,4 and through the tubes to their grounded cathodes as* af marking signal. When the switch opens under the influence of a negative voltage this, current is broken anda spacing-signal is produced in the connected circuit.

Attentionf-is,particularly calledv to the fact that the grids of tubes,` V53y and V54', Fig'.,6 are connected throughresistor R71v totheicathodes of these tubes. Hence when noV carrier is beingreceivedV from' the distant switchboard, since-thegrids'and cathodes of these tubes areV at the same potentiall and since lead TR is'terminated in` positive battery, inthe connected subscriber'station circuit, current will flow through the anode-cathode circuits of the tubes to hold the connected circuit in the marking condition; This is known as the'rnark-hold'feature; Reference to Fig. 5` shows that the arrangement of tubes V53 and V54 at the teletypewriter switchboard is the same asI at the oppositeterniinalconnectedto'the subscriber station. In this casewhen nocarrier is being receivedat the subscriber station, current will ow from positive 13G-voltl battery connected-to'lead S in the connected circuit through the anode-cathode ofthetubeV toground holdingthe connected circuit inthe marking condition.

. When the higher channel frequency is employed for spacing instead of marking, theleft-hand partl of the oscillating circuit of Fig. 5is made inductiveinsteadof capacitive andy thediscriminator switch dll-.is operated'to LF4}. This impressesfthe lower Vfrequency through rectiiier64and-the-resulting rectiiiedvoltage appears between pointsl XY.

When signals are being-transmitted from the switchboard, the subscriber station, Fig. 6, is normally trans#` mitting a steady marking signal, so that the grids of tubes V53 and V54 in Fig. 5 arefkept continually positive. These tubes will therefore conduct when a markng'signa'lfis transmitted from the switchboard byy closing the-circuit through conductor S, and will be nonconducting when a space is transmitted by opening the path through conductor S,- During the mark, grid 7 of tube 23 in-Fig. 5 is positive with respect toits cathode, causing` this tube to become conducting and to send out a marking signal over the carrier line'to the distant subscriber station.

scribersstation ya positivervoltage is applied to the grids of tubes V53 and V54, these tubes conduct and current iiows in conductor S.A This resultsin a voltage, applied toV the; grid of tube23,'in`E`g. j, which is positive During a spacing'signal the voltage atV grid 7 of tube 2,3, Fig. 5, which is connected to -l30' 9 respe'ct`to its cathode and marking frequencyH +11 is transmitted 'over'the carrier channel as described above to the distant subscriber station. When a spacing carrier signalis received by Fig. from the .distant sub` scriber station, a negative voltage is applied to the grids of tubes V53 and V54. This reduces the current in conductor S, in Fig. 5, to nearly zero. Thepotential at the plates of tubes V53 and V54 rises to +130l volts for this condition due to the battery not shown in Fig. 5

' but -apparent in Fig. l, at the end of conductor S. Thus the voltage applied to the grids of tube 23, Fig. 5, becornes even more positive and tube 23remains conducting so that an outgoing marking'condition is sustained. In summation, therefore, tube 23 of Fig. 5 cuts olf for a spacing signal from the switchboard through conductor S, conducts for a marking signal from the switchboard through conductor S, and remains conducting when a marking signal is received from the subscribers station as well as when aspacing signal is received from the subscribers station.

The resistor R13 shown in Fig. 5 is eifective in transmitting a break signal from the switchboard to the distant subscribers station. to transmit la break signal from the switchboard to the distant subscriber station, resistor 13 acts to insure that a spacing potential is applied to grid of modulator tube 23 in Fig. 5 during intervals when a spacing sign-al is being received from the subscriber-s station and tubes V53 land V54, in Fig. 5, are responsively cut off.

Normally battery is disconnected, as described, from the plate of oscillator tube at the subscribers station, when the station is idle and switch 9 lat the station is in its upper position. When switch 9 is actuated to its lower position, battery is connected to the anode of the oscillator tube 20, as also described, and marking carrier f1 is transmitted to the teletypewriterL switchboard. Switch 9 is actuated in order to operate the subscribers -line lamp at the teletypewriter switchboard. The manner in which the receiving branch of the carrier circuit in Fig. 5 functions to impose a condition on conductor RS so as to actuate the toll subscriber line circuit to light the lamp will now be described.

In response to the transmission of lmarking carrier f1,V

when switch 9 is actuated at the subscriber station, the carrier signal will be transmitted from Fig. 6, passed by receiving filter 31 in Fig. 5, tubes V51A and V51B and imposed on the input of tube V52 in Fig. 5, resulting in an lalternating-current flow from the plate of tube V52 through blocking condenser 70, resistor 71 land the parallel combination of resistor 73 and varistor 72 to the negative terminal of the filament battery, thence to ground and finally back to the cathode of tube V52. The rectifying action of varistor 72 sets up a directcurrent voltage across resistor 73 which opposes the negative 24-volt bias on the grid of tube 23. The lowpass R-C lter comprising resistor 75 and capacitances 76 and 77 shown in the grid circuit of tube 23 removes the carrier and provides a delay in the build-up of the direct-current grid voltage on tube 23'. Grid current flow in tube 23 `limits the voltage between grid and cathode to zero. When the rectified voltage across resistor 73 is equal to or greater than the 24 volt bias,

tube 23 conducts, since conductor RS is terminated inl positive 130-volt battery in the toll subscriber line circuit. Conductor RS extends through the winding ofthe supervisory relay SU 'in the toll subscriber'line circuit which controls the line lamp and performs other super-v visory function in a manner to be described. Whenthe carrier for the supervisory signal is applied to the input ofireceiving 'lter 31l at normal level, plate current does not ow'for about l5() milliseconds, but when the carrier input stops, theVV current .ilowing in the output circuit of tube 23 through conductor RS falls to zero in about 50 milliseconds. The longer delay insures against false operation Vof the supervisory relay due ,to bursts of noise,

When conductor S is open while the shorter delay-'provides va relatively fast dis`= connect signal when the distantV subscriber opens his power switch. y v

Refer now to the subscriber toll line circuit in Fig. -l.

Conductors S and RS Iare shown extending into the tolly Duringr the idle condition the transmission Alead S from the car` subscriber line circuit from Carrier Terminal 1.

rier channel terminal is connected through resistor RS, back contact 1 of relay C, back contact 1 of relay A and resistor RA to positive telegraph battery', whichm'ay be, for instance, 48 volts. Current which may be, for

instance, 20 milliamperes, will flow in lead S and the carrier channel terminal 'responsively will sendY out marking current to the line over the transmitting branch vof the carrier circuit to the distant subscriber station.

no relays in the subscriber toll'line circuit will be operated. It will now be assumed that the subscriber at the distant subscriber station calls the switchboard by oper- As av result of this, carrier current will be received through ating power switch 9 at the subscriber station.

SU. This current may be l0 to 15 milliamperes, for" instance, but its value is not critical. The operation of relay SU establishes a circuit from ground through contact 1 of relay SU and the winding of relay A to batteryf operating relay A. The operation of relay A will perform tive functions as follows:

(l) It transfers conductor S from contact f1 of relay A to contact 2 of relay A. Positive battery will, however, continue to be supplied to conductor S over a path through resistor RA, contact 2 of relay S and contact 2 of relay A, so that positive battery will remain connected to the conductor as in the idle condition.

(2) The operation of relay A, by opening its contact 3, will disconnect the winding of relay B from a path which is connectable to the ring conductor R of jack J2.

(3) 'I'he operation of relay A, by opening its contact 5, will disconnect ground from the tip conductor T of jack J 2. 1 l

(4) The operation of relay A will connect ground through its contact 4 and contact 3V of relay S, which relayy is unoperated, to the nightl alarm circuit. If a switch, not shown, in the night alarm circuit is inthe operate position, the night alarm circuit will be operated.

(5) The operation of relay A will close a circuit from battery vthrough its contact 6, contact 4' of relay S and the filament of line lamp L to ground, lighting the lamp as an indication that the distant subscriber is calling.

` The circuit is now ready for the connection of the plug PG2 of an answering cord to jack J2.

If the subscriber at the distant'subscriber station restores power switch 9.to its off or idle position and then reoperates it before the operator at the teletypewriter switchboard answers the call, first relays SU and A will release in sequence and the subscriber line lamp L at the switchboard will be extinguished in response to the restoration of the power switch to normal. Then relays SU vand A will be reoperated and lamp L will be relighted, thus following the operation of the power switch.

' If the subscriber at the distant subscriber station abandoristhe call by simply restoring the power switch to its of or idle position before the operator atthe switchboard answers, relays SU and A will release, the answering lamp L will be extinguished and the night alarm will be restored to normal.- Thus the subscriber toll line cirswersfan incoming call byv inserting plug PGZl of' an Noy current will flow in the supervisory conductor RSy and answering cordin the'linerjackf J2. The operation of the jack springs willperform three functions as follows:

(l) The operation of the jack springs will establish a circuit from battery, not shown, in the cord through the sleeve of plug PGZ, sleeve ofjack J2, lead SL and the winding of relay S t'o ground operating relay S. lt will also operate relays, not shown, in the connected cord circuit to set up a transmission path in the cord.

(2) The operation of relay S-by opening its contact 4 will extinguish subscriber line. lamp L.

(3) The operation of relay S, by closing its contact l and opening its contact 2, will transfer the transmission lead from positive telegraph battery through resistor RA to positive telegraph battery of the same potential, not shown, in the cord through` the ring lead R of the jack and the connected ring lead of the cord. The operators teletypewriter set will be included in this path if the typing key of the cord circuit is operated. This path was establishedV by the operation of relays in the cord circuit when. the sleeve leadof the cord circuit was connected, as described under function l of this section. Other circuit functions in the cord circuit prevent interference as two operators answer the same incoming call. Attention is particularly called to the fact that the operation of the cord circuit is described in detail in patents identified in the foregoing.

The operator may now operate the typing key in the cord circuit and communicate with the subscriber at the distant subscriber station. Keyboard operation of the operators teletypewriter will open and close the path through conductor S which will cause alternate spacing and marking carrier current to flow in the line to the subscriber. The same operation will take place in the reverse direction from the subscriber to the operator.

The subscriber at the distant subscriber station may recall the operator after the operators connection to the line jack has been made by restoring power switch 9 at the subscriber station to its off or normal idle position and then again reoperating it.

The operation of the power switch 9 to its off or normal idle position will interrupt the flow of current in conductor RS. This will release relays SU and A, leaving relay S operated, as it is assumed that the operators cord circuit remains connected to jack J2. The tip lead T of the cord circuitv will be connected to ground through contact 5 of relay A. This causes a relay in the cord circuit to operate which lights the cord answering supervisory lamp, and prepares the cord for subsequent functions when ground is disconnected from the tip` lead.

The -operation* of power switch 9 to its operated position will cause currentto ilow again in conductor RS. This will reoperate relays SU and A. This will reconnect the ring conductor R of the cord circuit to the transmission lead S at contact 2 of relay A. It will also open the tip lead of the cord circuit by opening contact 5 of relay A.l As a consequence of this, the release of a relay in the cord circuit will connect interrupted ground to the cord lamp, not shown, causing it to ash as a recall signal, to indicate that the distant subscriber is recalling the operator at the switchboard. The switchboard operator may extinguish the flashing cord lamp and reply to the subscribers recall 'signal by operating the typing key in the cord circuit. This will reconnect the operators teletypewriter in the path of the ring lead of the cord circuit and the dashing of the cord circuit lamp will cease. The switchboard operator may complete the call by connecting her calling plug PGl to the proper jack I1, after securing the necessary information from the calling subscriber.

If the subscriber at the distant subscriber station wishes to disconnect, power switch 9 at' the subscriber station is actuated to its upper or off position. This interrupts the ow of current inconductor RS and releases relays SU and A. The release ofv these relays produces the samer circuit` action las doesv the start of a recall signal,

described in the foregoing. Since theV power switch in this case, however, is not reoperated, the cord lamp will remain steadily lighted, the ring of the cord circuit will remain open, the tip of the cord circuit will remain grounded and conductor S to Carrier Terminal 1 will remain connected to positive telegraph battery through contact 1 of relay A.

The switchboard operator may ring or re-ring the subscriber without disturbing the connection, by operating the ringing key in the cord circuit. The grounded tip of the cord circuit at contact 5 of relay A will permit circuit operations in the cord circuit which result in the application of ringing current to the ringing lead R of' the cord circuit. With relay S operated and relay A released, this ringing current will pass through contact 1 of relay S, contact 3 of relay A, winding of relay B and ringing condenser RC to ground. Relay B will be oper'- ated and released at the frequency of the ringing current. The operation of relay B will establish a circuit from ground through contact l of relay B and the winding of relay C to battery, operating relay C. Relay C is a slowto-release relay and remains operated throughout the ringing period. The operation of relay C by openingits contact l and closing its contact 2, will transfer trans=l mission conductor S from the ring, of the cord circuit to the ringing circuit, which extends through the lament of ringing lamp RL to a source of ringing current. This, in turn, will cause the ringer at the subscriber station to operate.

The subscriber at the distant subscriber station will answer the ring or re-ring by operating power switch 9 to its lower or operating position. This will restore `the current in conductor RS in the subscriber toll line circuit' and the circuit action will extinguish the cord lamp as an indication that the station attendant has answered.

After the subscriber has disconnected, the operator at the switchboard may disconnect by removing the plug PGZ of the answering cord from the line jack I2. The disconnection of the answering cord will perform four functions as follows:

(l) It will open the sleeve lead SL.

(2) The opening of the sleeve lead SL will release relay S.

(3) The tip lead T will be opened.

(4) The ring lead R will be opened.

The release of relay S will perform two functions as follows:

(l) It will close the circuit from the subscriber line lamp L through contact 4 of relay S. This path, however, will be opened at contact 6 of relay A.

(2) The closing of contact 3 of relay S will connect the night alarm circuit to contact 4 of relay A which is opened.

The foregoing vrestores the idle condition for both the subscriber toll line circuit and its cooperating cord circuit.

To originate an outgoing call or to complete an incoming call, the operator will insert the plug PGZ of her calling cord into a called subscriber line jack, such as jack J2, after making a busy test.

The operator may make a busy test of the subscribery line by touching the sleeve of the line jack with the tip of the calling plug PGZ. If the line is busy, the sleeve 'of the line jack will be carrying a negative potential from the sleeve of the connected cord. This potential, when applied to the tip of the subsequently connected cord circuit, will light a busy test lamp in the operators busy test circuit.

When the switchboard operator establishes a connection to a called subscriber line, the plug PGZ of the calling cord is inserted in the called subscriber line jack I2. This performs three functions as follows:

( 1) It connects the sleeve lead of the cord circuit through the winding of relay S to ground. This will operate relay S and will also operate relays in the cord circuit to prepare it for subsequent ringing operations.

(2)It will connect thevtip leadvofthe cord crcuit'to ground through back contact'S- of relayvA.

(3) It will connect the'ring lead of the cord through contact 1 of relay S and the direct-.current path of the ring lead will be open'at contact 2 of relayA. As seen from Athe 'connected carrierchannel terminal, con-` ductor S will be terminated in positive 48-volt, telegraph battery, for instance, through contact 1 of relay A vand reSStOrRA-- Y r Y,

The operation .of relayS willl performl -three functions asfollows;v Y(un tact 4 ofrelay S.

1.2)- n wmppenihsngilt 'aan naa.

to therwinding ofvrelayB`= through Acontact 1 of relay S and contact 3 ofrelay A audjwill remove rpositivebattery VThe grounded .tiplcad Tofthecord circuit will permit the application of ringing current to the ringlead of thek The operation ofi re1ay',B willjoperate theleslowy-to-l release relay'C which wil remain operated during the ringinginter'val.Y The operation of relay C will connect ring-v ing current to conductor S whichiertends into Carrier Terminall and, responsively, the ringer at the subscriber station willbeY operated.. I Y

In the` cord circ f't, the operation of the ringing key will light and extinguish aringing guard lamp, not shown, in cycles, Suchas, for instance, two seconds.lighted and four seconds extinguished per cycle.

ringing by operating powenswitch 9 to its lower position. This will causecurrent toy ilow in conductor RS of the subscriber toll line circuit` and'will operate Arelay SU as heretoforedescribed.-

At the subscriber station, the operationr 'of power switch 9 will disconnect the ringing equip the subscriberteletypewriter.

The operation of relay SU in the subscriber toll line circuit will operate relay, The operation of relay A will perforn-threcfunctions as follows: o

(1) It willj-,disconnect 4.thring lead Rof the cord circuit from the winding of relayWBby opening contact of relayA. .o

(2) It will disconnect rthe tip lead of the cord circuit from ground by contactjS of relay A.

(3) It connect thering conductor R to ,transmissioneonductorS by closing'contact 2 of relayk A( 7The removal of ground fr ornthe tip lead T'of. the cord circuit, by the opening of"coi1tact 5 of'relay A, will extinguish the ringing guard lamp circuit and prepare the ring lead of the cord circuit for transmission. The two subscribers, or the operator yand either subscriber, may now communicate by teletypewriter over the ring lead of the cord circuit.

ment which is normally connectedto the line and connect 'I'he called subscriber may recall the operator by actuatcircuitV lop-ent k coilductor of line lamp L atv'con-I ',Ifhe'subscriberaat Athe distant station 'will' answer the` toftthe. teletypewr-iterfswitchboard by actuating power"-l 9-iin;the subscriber station circuit 'at the calledf st rbscriber.y Station to its upper position. This operation is4 Switchf thel `same asdescribedffor disconnect by a calling' sub# sciber, vexcept that .apparatus in the calling side of the cord. functions, instead of, apparatus in 4the answering side` ,f Transmissiomthrough toll subscriber-line circuit is carried jon `over conductor.;S; and 'the ring lead of the crnfdcircuit with; marking vcurrent whichr may, for instance, be2() mil-liamperes and spacing'current of zero,

respectivelyf. i'

Ig'\ l1e rtrans miss ionoflbreak signals through this in either direction is performed by interruptingcurrent l in conductor` Se.; The -ln'eal signal is transmitted through the cordfcircuit repeater in .the conventionalrnannen f Attention is now calledto. the distinguishing character istics 'between carrier terminals locatedjat the ends ofl the; linejand carrier terminalslocated at Tintermediate` In an arrangement, for instance, in which Carr;

points. rier-Terniinal l1 at lthe switchboard is connected to Carrier 'I" er rr' x i nal,l 2 1atthe'subscrilzyer station, the signals trans-.i mitted Afron1 tl 1e switchboard toward the "subscriber station, and 'from the'-s1 1l asc :riber` station toward the switchboard; areY-conyertedfrm alternating current to direct-currentr l .tl; ie present invention, two carrier terminals locatedl atv-intermediate points, Carrier Terminals 3 and 4 arev interconnected bachftback in such manner that the sig-` nalspas` si ngf through the lreceiving branch of each may bejetlectively impressed `o n thetransmitting branch of thether WithoutI the necessity for introducing a special repeaterdesigned to Aconvert the current signals into po- Y tentiial changes.

How this is performed will now be explained.A

YCarrier,Terminal 3 is in accordance with Fig. 3. and-1. Carrier Terminal 4 is in accordance with Fig. 4. In` eachkof these figures, the: sending path and the receivingY path,l instead of being joined together at the input o f the. sendingpath and the output of the receiving path, as is the case in CarrierTerminal 1 and Carrier Terminal Z,V

are separated. 1

The conductor in Veach of Figs.- 3 and 4 is connected tothe mid-point of 'an individual potentiometer, and the inputof the send-.1

ing lbr'anchof the `carrier terminal, to which the signals are to be propagated, is connected 'to the same junction.

For this purpose two dpotentiometer circuits are provided,

as shown 'in Fig. l1. One of these circuits may be traced' from. battery rthroughresistor PTRl, junction J4 and Iresistor PTRZ to ground. The other` may be traced from Y battery through kresistor vAPIIRS,ju1'1ction'J3l and resistor P'I`R4 lto ground. Out-put conductor XX of Fig. 3 connects rto junction J 3 and input conductor ZZ of Fig. 4 connects to the same junction I3. Output conductor YY of Fig. 4 and input conductor RR of Fig. 3 similarly connect to terminal J4. The relative values of the resistors and rthe magnitudes and polarity of the potential of the battery connected thereto are such that the proper poteniti-als are applied to the input circuit of the modulator drive tube Z3 in Fig. 3 and Fig. 4 so that this tube in each figure is yactivated and cut off in response to signaling conditions applied thereto.

The cathode of sending tube 23 in each of the carrier terminals is biased by :the voltage divider to a potential considerably more positive, 40 volts more positive, for

at the output of the receiving branch 11"'5 g instance, tnanthje potentiel fe'f the estuaries 'die receiving tubes such as ltubes V53 land V54 in each carrier terminal, `so that, when fthey 'arearriangedasfare ACarrier position. When in the HM position the circuits "ar'ejar-` ranged' as sin Fig. '5 and Fig. lin'vvhichno 'entrespendingv When a `backto-'back connection 'is employed'fat lan intermediate point, means'must ibeprov'idedflto propagate line 'calling Vand supervisory signal conditions, generated Iatth'efsubscribersstation betWeen'Cifrie'r Terminal Y'3 Carrier Terminal 4. This is performed in the *following manner: y

' `A circuit v'is provided whichl'rnay be tracedjin Fig. 1 from ipositive Jbattery through the winding o'flrelaySU-BB and conductor H, which -entends 1intoliig. 3, and fromthe anode to the lcathode of supervisry "signal =tube `23' in Fig. -3 to ground. While carrier is vbeing-transitiitte'dffro'nr rthe `switchboard and -at all 'times except-When =it is linterrupted for `an interval of vsu'ficient duration, relay 'SUBB wil-l be operated. When the carrier is interrupted vfor. the transmission of a line `calling Yor supervisory-signal, relay SUBB Will rrelease opening its signal contact. `Vhile relay SUBB is operated, -a circuit may be traced vfrom positive battery in Fig. 1 through the Contact Lof 4relay SUBB and conductor C 'which 'eX'tend-s- -into Pig. f4 yand through resistor R9, "the yanode-cathode ,circuit of oscillator tube Z vand resistors R3, R2 4a'n'l R-1=`to ground. Under tliis condition oscillatorjtube "20 will oscillate. When the Contact of relay SUBB is opened, oscillations in tube 20 will cease. Signals produced yin the upper or transmitting branch of C-arrier 'Terminal Vl-,Will 'be transmitted 'to Carrier Terminal `1 and pass "through cthe receiving branch `thereof and the subscriberj'toll line -circuit t`o lthe switchboard in a ymanner which should be understood from the foregoing.

All of the signal conditions described in the foregoing vvhich '-may be transmitted Vfrom a Vsubscriber"station to a teletypewriter switchboard when 'they-are ldirectlyinterconnected from a 'carrier 4terminal'at the ysubscriber station to a carn'er terminal and subscriber toll line circuit at the Vswitchboard may, by mea-nsjof the 'present invention, beV transmitted also through an intermediate Yrepeating point, v vhereat two carrier terminals are interconnected backito-back.

The same general method 'as described in-the Aforegoingv series with leea This ffeiy venia-.lin ftumeemrithe oscillator in Carrier Terminal Iin'-'z'vrnaniierfxtiliicll graph channel interconnecting saidr frst directcurr'ent:

circuit, in tandem, `through lsaid Hirst, secnd,"third and fourth terminating circuit to said second direct-current circuit, a rst potentiometer circuit "5in said "channel intrconnecting '-an output of second 'terminating Lcircuit to an input of said terminat'iijg circuit, `-a` lsecond potentiometer circuit in said channel interconnecting output of said third 'terminating circuit to an "input let said second terminating circuit and means connected to each of said potentiometer circuits Efor,translating incoming current-no-current signals into outgoing potential Signals- 2. A system in accordance withclairnv l, said system having means for v`trans'imitting telegraph communication signals and means for transmitting line calling signals thefreVe'l. Y I Y 3. A system 'in accordance with "claim 1, `said 'system having Vmeans Jifo'r transmitting VV`recall thereover.

4. A system in accordancc'with 1, 'said system having means for transmitting line calling signals 'thereover and other l"m'cans for transmitting spervisdry signals thei'over. i p p 5. A first, second, ith'ird and '-fourthjcarrier-jcurrent-'dif rect-current terminating circuit, leach of'said 'circuits rhaving means for Areceiving *directement telegraph signals. and translating -them into a'lte'rnating-f'current signalsV 'and vice versata rstand a seconddirectcurrent telegraph `crcuit, a two-way operative telegraph -tilia'ririel interconnecting said iirst directcurrent circuit, "in"tai1rdem, through said li'irst, second, third `and fourth tei'ninatirrg circuit in named order to said second 'directcurrent c'ir'cuit, 'said channel having a rst potentiometer circuit interconnecting the output of a space discharge 'device 'ina 'receiving branch in saidsecond terminatingcircuit tofthe'inputofa space discharge device lin a sending branch 'insai 'third terminating Acircuit and a second potentiometer cir'cultiir'iterconnecting the output fof Va `space discharge dfvice liria receiving branch in said terminating circuit tothe input of a space discharge 'device ina sending Branch in said second `terminating circuit.

References Citeavin theme ef-tniepatent Y UNITED sTArEs PATENTs 2,502,942 Gooden Apr; 4, i956 Gardner ANov.':13, '19"56r November 13949, (Copy Division 42S).Y

by B. Ostendorf, Jr., ALLEE., Technical-Paper ses, 

